Work will be concentrated primarily in the following areas: 1. Pathogenesis of immune thrombocytopenias; detection of platelet antibodies; characterization of platelet auto- and iosantigens. Methods of detecting iso-, auto-, and drug-dependent antibodies reactive with human platelets will be further refined with particular attention to techniques involving 51Cr release and binding of 125I-anti-IgG antibody. Expression of HLA antigens on platelets and its genetic control will be characterized. Platelet membrane antigens will be solubilized and purified and their alloantigenic markers will be identified. Guidelines for "matching" of platelets for alloimmunized recipients will be further defined. 2. Molecular basis of the platelet "storage lesion". Biochemical and strucutral changes occurring in platelets during short-term storage will be further characterized. Priority will be given to adenine nucleotides, glycogen, and membrane glycoproteins. 3. Improved yield of Factor VIII in cryoprecipitate. Ways of identifying blood donors whose plasma contain above-normal levels of Factor VIII will be sought. Variables affecting the yield of Factor VIII in cryoprecipitate will be studied and findings applied to production of a a higher potency, lower cost, preparation for the treatment of hemophilia.